1. Field of the Invention
This invention relates generally to valve lifters, and more particularly to an adjustable hydraulic valve lifter.
2. Description of Related Art
The following art defines the present state of this field:
Aoyama, U.S. Pat. No. 4,218,995, teaches a hydraulic valve lifter mechanism that includes a second chamber in a manner similar to the present invention. Oil in the second chamber is regulated with a piston and an oil-reserving chamber. Under the right circumstances, the oil-reserving chamber will allow oil to escape from the second chamber. When oil pressure applied to the first chamber is decreased as the engine speed lowers, the plunger moves toward the first chamber to allow the second chamber to communicate with an oil-reserving chamber through a hole. The amount of valve lift in a medium oil pressure range depends on the degree of closing of this hole by the plunger which is moved together with the cylinder head by the rotating cam.
Butler, et al., U.S. Pat. No. 4,407,241, teaches an expandable hydraulic tappet having a variable exit valve for use in an internal combustion engine to selectively vary timing by altering the effective profile of a camshaft. The tappet expands to extend the drive train between the camshaft and a camshaft operated mechanism by enlarging and filling an internal hydraulic chamber with a non-compressible hydraulic fluid via an inlet port and inlet valve. The fluid is retained in the tappet chamber until a predetermined pressure is attained, when an exit valve opens to exit the pressurized fluid from the chamber at a predetermined rate. The exit valve (94) preferably includes a bore having a predetermined (stepped) configuration to provide one or more exit flow rates and also dampen valve operation. An exit valve control means responds to the pressure within the hydraulic chamber to open and close the exit valve and vary the flow rates as desired.
R. C. Shunta, et al., U.S. Pat. No. 3,385,274, teaches a push rod and rocker mechanism having a variable stroke hydraulic tappet interposed between the push rod and cam. The tappet has a plunger drivably abutting the push rod and drivable in turn by a piston-like inner member by resting on a column of hydraulic fluid contained in an outer cylinder like member which drivably engages the cam. The hydraulic fluid is supplied under adjustably controlled pressure from a pump to a port in the outer member which is open only between lift strokes of the tappet, i.e. during the dwell and lower portions of the cam lift cycle.
Other similar examples are shown in the following references: Yagi, et al., U.S. Pat. No. 4,889,085 (valve operating device), Rhoads, U.S. Pat. No. 4,741,298 (rollerized timing valve lifter), Aoyama, U.S. Pat. No. 4,324,210, Rhoads, U.S. Pat. No. 4,524,731, Rhoads, U.S. Pat. No. 4,602,597, Bruton, U.S. Pat. No. 5,623,898, Rendine, U.S. Pat. No. 3,724,921, B. C. Skinner, U.S. Pat. No. 2,803,231, Rhoads, U.S. Pat. No. 4,601,268, and Rhoads, U.S. Pat. No. 4,977,867.
The above-described references are hereby incorporated by reference in full.
The prior art teaches hydraulic valve lifters that are to some degree adjustable. However, the prior art does not teach an adjustable hydraulic valve lifter that can be continuously adjusted during operation to accommodate various different operating conditions using the mechanism described herein. The present invention fulfills these needs and provides further related advantages as described in the following summary.